WO2000012366A1 - Braking device with combined power-assistance and control - Google Patents

Abstract

The invention concerns in particular a braking device comprising: rear and front pressure actuators (21, 22); mechanically and electrically controlled pressure generators (31, 32); and control magnet valves (61, 62, 63). The invention is characterised in that the front pressure actuator (22) input (222) is directly connected to the electrically controlled pressure generator (32) output, while a control magnet valve (61) selectively connects the mechanically controlled pressure generator (31) output (313) to the front pressure actuator (22) input (222), the pressure delivered by the electrically controlled pressure generator (32) capable of being electrically modulated.

Description

 BRAKING DEVICE WITH COMBINED ASSISTANCE AND REGULATION

The present invention relates to a braking device for a motor vehicle, of the type which makes it possible to avoid the locking of the wheels of this vehicle.

More specifically, the present invention relates to a braking device for a vehicle, of the type which includes a closed hydraulic circuit, filled with a hydraulic fluid selectively subjected to different pressures at different points of the circuit, this circuit comprising. a low pressure tank; a first pressure receiver associated with a rear wheel of the vehicle and whose input constitutes a first point of the circuit; a second pressure receiver associated with a front wheel of the vehicle and whose input constitutes a second point of the circuit; a first pressure generator mechanically controlled and whose output constitutes a third point of the circuit; a second electrically controlled pressure generator, the output of which constitutes a fourth point of the circuit; a hydraulic fluid accumulator; a pressure sensor capable of providing a measurement of the pressure of the fluid at the third point of the circuit; and valve means.

Devices of this type are well known in the prior art and used for many years. One of the problems encountered in the design of such braking systems lies in the difficulty of constantly improving their performance while reducing the cost, in particular to allow the widest possible distribution and thus ensure optimum safety for the greatest possible number of vehicles. The present invention is situated in this context and aims in particular to allow a significant reduction in the cost of manufacturing devices of this type by optimizing their functions.

To this end, the device of the invention, moreover conforms to the definition given in the preamble above, is essentially characterized in that the second and fourth points of the circuit are connected to each other for be permanently subjected to the same pressure, in that the valve means comprise a first solenoid valve controlled to change from a passing state in which it connects the second and third points of the circuit to one another, towards a state blocking in which it isolates from each other the second and third points of the circuit, in response to a crossing, by the pressure measurement, of a predetermined threshold, and in that the pressure delivered by the second generator of pressure is electrically adjustable.

Preferably, the accumulator is provided with an inlet directly connected to the third point of the circuit, and this accumulator is pre-adjusted to admit hydraulic fluid only when the fluid pressure at the third point of the circuit is at least equal to the three quarters of said predetermined threshold.

In a braking device in which a first absorption law links each variation in the volume of fluid admitted into the accumulator to a corresponding variation in the pressure of the fluid at the third point of the circuit, in which a second absorption law links each variation in volume of fluid admitted to the second pressure receptor to a corresponding variation in the fluid pressure at the fourth point of the circuit, and in which the first and second absorption laws have respective first and second slopes, these first and second slopes advantageously have a ratio of between 0.75 and 1.33.

To further optimize the braking device of the invention, it is preferable to provide that the valve means further comprise a second solenoid valve selectively connecting the first and third points of the circuit, and a third solenoid valve selectively connecting the first point of the circuit to the low pressure tank, the second and third solenoid valves allowing a selective modulation of the pressure in the first pressure receiver.

Conventionally, the first pressure generator can comprise a master cylinder, associated or not with a vacuum booster.

The second pressure generator can in turn comprise a piston mounted to slide in leaktight manner in a cylinder and selectively driven by an electric motor.

Thanks to these characteristics, the device of the invention can combine the advantages of variable assistance on each front wheel of the vehicle with the advantages of an anti-lock regulation on each rear wheel, without having to resort to the use of 'a pump.

It is thus possible, in particular: - to respond to emergency braking conditions with variable assistance on each front wheel;

- to maintain and / or improve the response times of the braking device thanks to the direct connection between the master cylinder and each pressure receiver in the initial phase of a braking sequence; - to keep the usual pedal feeling, the usual dead travel, and the usual triggering threshold of a standard braking device, by equipping the device of the invention with a reduced-pressure vacuum booster;

- to control manufacturing costs by simplifying the anti-lock braking function on the rear axle of the vehicle; - And to obtain increased security by the use of two energies, namely muscular and electrical energies, and by duplication of the pressure generators controlling the front pressure receptors.

Other characteristics and advantages of the invention will emerge clearly from the description which is made of it below, by way of indication and in no way limiting, with reference to the appended drawings, in which:

- Figure 1 is the diagram of a braking device according to the invention; - Figure 2 is a diagram representing the laws of absorption of the accumulator and the pressure receiver of the front wheel;

- Figure 3 is a diagram representing, as a function of the braking force exerted by the driver of the vehicle, the evolution of the hydraulic fluid pressures in the front and rear receivers, for a braking device according to the invention, provided a brake booster vacuum booster; - Figure 4 is a diagram representing, as a function of the braking force exerted by the driver of the vehicle, the evolution of the hydraulic fluid pressures in the front and rear receivers, for a braking device according to the invention, not equipped with vacuum brake booster; and

- Figure 5 illustrates a possible embodiment of the second pressure generator.

The invention relates to a braking device for a motor vehicle making it possible to prevent the wheels of this vehicle from locking up.

More specifically, the invention relates to a braking device for a vehicle, of the type which includes a closed hydraulic circuit, filled with a hydraulic fluid selectively subjected to different pressures at different points of the circuit. Such a circuit conventionally comprises: a low pressure tank 1; pressure receptors such as 21, 22, respectively associated with the rear and front wheels of the vehicle, and each of which is capable of applying to the corresponding wheel a braking torque depending on the pressure which it receives; a pressure generator 31 controlled mechanically by the muscular work of the driver of the vehicle; an electrically controlled pressure generator 32; a pressure sensor 5 providing a pressure measurement signal Mp; and solenoid valves such as 61, 62, and 63.

Wheel sensors (not shown) supply a logic unit 7 with signals RI, R2, R3, and R4, each of which is representative of the rotational movement of a corresponding wheel of the vehicle, the logic unit also receiving the measurement signal pressure switch Mp and delivering control signals S32, S61, S62, and S63 to the pressure generator 32 and the solenoid valves 61, 62, and 63.

Readers unfamiliar with the technique concerned can advantageously refer to the technical booklet of the depositor, entitled "Braking devices for cars" and published by Editions Delta Press, 35, Rue Sainte-Cécile, 13005 - Marseille, France.

A first point of the hydraulic braking circuit is constituted by an inlet 211 of the first pressure receiver 21; a second point of this circuit is constituted by an inlet 222 of the second pressure receiver 22; a third point is constituted by an output 313 of the pressure generator 31 with mechanical control; and a fourth point of this same circuit is constituted by an output 324 of the electrically controlled pressure generator 32. The pressure sensor 5 is directly installed at the third point 313 of the circuit in order to be able to supply, as a signal Mp, a measurement representative of the fluid pressure at this third point 313.

According to a first aspect of the invention, the second and fourth points 222, 324 of the circuit are directly connected to each other so as to be permanently subjected to the same pressure.

At rest, that is to say in the absence of actuation of the braking device, the solenoid valve 61, which is installed between the second and third points 222, 313 of the circuit, is in a passing state such that 'illustrated in Figure 1 and in which it communicates between them these second and third points 222, 313 of the circuit. When the pressure measurement Mp crosses a predetermined threshold Sp, this crossing is detected by the logic unit 7 which immediately controls the passage of the solenoid valve 61 in a blocking state, in which this solenoid valve isolates them from each other. second and third points 222, 3 13 of the circuit.

The second pressure generator 32 is moreover of the type of those which deliver an electrically adjustable pressure.

Under these conditions, it is possible, as soon as the driver has applied a pressure equal to the threshold Sp, to use electrical energy to intensify the braking effort without requiring, on the part of the driver, an additional muscular effort that he may not be able to provide.

According to a second aspect of the invention, the accumulator 4 is provided with an input 43 directly connected to the third point 313 of the circuit, and this accumulator 4 is preset to admit hydraulic fluid only when the pressure of fluid at the third point 313 of the circuit is at least equal to three-quarters of the predetermined threshold Sp, and, more advantageously still, when it is equal to this threshold Sp. To this end, the accumulator 4 may include a spring 41 which pushes back a piston 42 and which is compressed when the piston is moved by the fluid entering the accumulator, the spring 41 being prestressed so as to allow the admission of fluid only beyond the desired pressure. Thanks to this arrangement, it is not only possible to use the accumulator to simulate the actuation of the second pressure receiver 22, as if the solenoid valve 61 had remained in the on state, but also to store in the accumulator 4 a certain volume of pressurized fluid usable to operate an anti-blocking regulation without pump of the first pressure receptor 21.

To do this, it is necessary to make coincide at least approximately, for pressure values greater than the threshold Sp, the first absorption law defined as being that which links each variation in volume VI of fluid admitted into the accumulator 4 to a corresponding variation in the pressure PI of the fluid at the third point 313 of the circuit, with the second absorption law defined as being that which links each variation in volume V2 of fluid admitted into the second pressure receiver 22 to a corresponding variation in the fluid pressure P2 at the fourth point 324 of the circuit.

In reality, as shown in Figure 2, the second absorption law first presents a non-linear evolution which corresponds to the catching up of the clearances, and which is followed by a linear evolution defined by a slope K2, corresponding to the deformation elastic of the brake actuated by the pressure receptor 22.

The first absorption law is a linear law of slope Kl, where Kl is the stiffness of the spring 41, whose origin in pressure PI is located at the value of the threshold Sp, whose origin, measured in volume V2 , is noted Vs, and whose origin, measured in volume VI, is zero, since the volume of fluid VI admitted into the accumulator only begins to increase for the values of the pressure greater than the threshold Sp. Under these conditions, filling the accumulator 4 can provide an optimal simulation of the actuation of the pressure receiver 22 provided that the threshold Sp is chosen on the linear part of the second absorption law and subject to giving the stiffness Kl of spring 41 the value of the slope K2 of this second absorption law, this simulation remaining acceptable as long as the ratio K 1 / K2 remains between 0.75 and 1.33. As the accumulator 4 constitutes a reserve of pressurized fluid available for the first pressure receiver 21, it is possible to modulate the pressure prevailing in this first pressure receiver without having to resort to the use of a pump.

To this end, it suffices, as shown in FIG. 1, to provide a second solenoid valve 62 installed between the first and third points 21 1, 313 of the circuit, and a third solenoid valve 63 installed between the first point 21 1 of the circuit and the low pressure tank 1, these second and third solenoid valves 62, 63 being controlled by the logic unit 7 to allow selective modulation of the pressure in the first pressure receiver 21, in particular to avoid blocking of the corresponding rear wheel.

As shown in FIG. 1, the first pressure generator 31 can comprise a master cylinder 31 1, whether or not equipped with a vacuum booster 312.

FIG. 3 is a diagram representing, as a function of the braking force F exerted by the driver of the vehicle, the evolution of the pressures P22 and P21 in the front receivers 22 and rear 21, in the case of the use of a vacuum servo motor 312.

The pressure P21 in the rear pressure receiver 21 changes as a function of the force F according to the characteristic response curve of the servomotor, unless for example this pressure must be regulated by the switching of the solenoid valves 62 and 63 in order to momentarily block of the corresponding rear wheel, this situation being illustrated by the change in pressure P21R.

The pressure P22 in the front pressure receiver 22 being, up to its threshold value Sp, generated by the pressure generator with mechanical control 31, it follows, in the absence of any regulation, the same evolution as the pressure P21.

On the other hand, insofar as, beyond the threshold Sp, the pressure P22 is generated by the electrically controlled pressure generator 32, this pressure P22 can both substantially exceed the pressure that the force of the conductor makes appear at the third point 313 of the circuit, and change independently of the pressure available at third point 313, the pressure P22 can itself be modulated by electrical control of the pressure generator 32, for example to momentarily block the corresponding front wheel, as shows the P22R evolution of this pressure. In the case where no servomotor is used (FIG. 4), the situation is similar, except that the pressure P21 changes along the response curve characteristic of a master cylinder devoid of any assistance.

As shown in FIG. 5, the electrically controlled pressure generator 32 advantageously comprises a piston 321 slidably mounted in a sealed manner in a cylinder 322 and selectively driven by an electric motor 323, for example by means of a reducer with gear train 325 and a screw-nut connection 326, a piezoelectric pressure generator can however be used in place of the generator illustrated.

Claims

1 braking device for a vehicle, of the type which includes a closed hydraulic circuit, filled with a hydraulic fluid selectively subjected to different pressures at different points of the circuit, this circuit comprising a low pressure reservoir (1); a first pressure receptor (21) associated with a rear wheel of the vehicle and whose input (21 1) constitutes a first point of the circuit; a second pressure receiver (22) associated with a front wheel of the vehicle and of which an input (222) constitutes a second point of the circuit, a first pressure generator (31) controlled mechanically and of which an output (313) constitutes a third point of the circuit; a second pressure generator (32) electrically controlled and an output (324) of which constitutes a fourth point of the circuit; a hydraulic fluid accumulator (4); a pressure sensor (5) capable of providing a measurement (Mp) of the pressure of the fluid at the third point (313) of the circuit; and valve means (61, 62, 63), characterized in that the second and fourth points (222, 324) of the circuit are connected to each other so as to be permanently subjected to the same pressure, in that that the valve means (61, 62, 63) comprise a first solenoid valve (61) controlled to evolve from a passing state in which it connects the second and third points (222, 313) of the circuit to one another , towards a blocking state in which it isolates from each other the second and third points (222, 313) of the circuit, in response to a crossing, by the measurement (Mp) of pressure, of a threshold (Sp ) predetermined, and in that the pressure delivered by the second pressure generator (32) is electrically adjustable. 2. Braking device according to claim 1, characterized in that the accumulator (4) is provided with an input (43) directly connected to the third point (313) of the circuit, and in that this accumulator (4) is preset to admit hydraulic fluid only when the fluid pressure at the third point (313) of the circuit is at least equal to three quarters of said predetermined threshold (Sp). 3 Braking device according to claim 2, characterized in that a first absoφtion law links each variation in volume (VI) of fluid admitted into the accumulator (4) to a corresponding variation in the pressure (PI) of the fluid at the third point (313) of the circuit, in that a second absoφtion law links each variation in volume (V2) of fluid admitted into the second pressure receiver (22) to a corresponding variation in the pressure (P2) of fluid at the fourth point (324) of the circuit, in that the first and second absorption laws have respective first and second slopes (Kl, K2), and in that the first and second slopes have a ratio (K1 / K2 ) between 0.75 and 1.33. 4. Braking device according to any one of the preceding claims, characterized in that the valve means (61, 62, 63) further comprise a second solenoid valve (62) selectively connecting the first and third points (211, 313) of the circuit, and a third solenoid valve (63) selectively connecting the first point (211) of the circuit to the low pressure tank (1), the second and third solenoid valves (62, 63) allowing a selective modulation of the pressure in the first pressure receiver (21). 5. Braking device according to any one of the preceding claims, characterized in that the first pressure generator (31) comprises a master cylinder (311). 6 Braking device according to claim 5, characterized in that the first pressure generator (3 1) comprises a vacuum booster (312) 7 Braking device according to any one of the preceding claims, characterized in that the second pressure generator (32) comprises a piston (321) slidingly mounted in a sealed manner in a cylinder (322) and selectively driven by an electric motor ( 323)